Carrier 50PD05 Operating And Service Instructions page 19

For
all units with Economizers:
1. 1.The outdoor temperature is below the Econo Cool Hi
Temp Limit (Configuration--_ECON--_EH_LO) and above
the Econo Cool Lo Temp Linfit
(C onfiguration--+ E CON--+ EL_LO) .
For units with Enthalpy Control
2. 1.The outdoor enthalpy is low and the outdoor temperature
is below the Econo Cool Hi Temp Limit
(Configuration--+ECON--+EH.LO) and above the Econo
Cool Lo Temp Limit (Configuration--+ECON--+EL.LO).
If the conditions above are true and the economizer is available for
cooling the economizer outside air and return air dampers will
modulate to allow proportions of outside air and return air to mix
and produce a temperature equal to the Cool Supply Air Set Point
(Setpoint--+SASP). If reset is applied to the Supply Air
Temperature Set Point (Setpoint--+SASP) the dampers will control
to the Supply Air Control Point (Run Status--+COOL--+SA.CP).
If the conditions above are true but the economizer dampers are not
able to satisfy the Cool Supply Air Set Point (Setpoint--+SASP)
with Reset (if applied), the compressor will turn on and modulate
to provide additional cooling to satisfy the Cool Supply Air Set
Point (Setpoint--+SASP) with Reset if applied.
If the conditions above are not true, the economizer will move to a
user Configurable Econ Min at Max Fan Speed
(Configuration---,ECON---,MP_X) where the nfinimum
economizer damper position is based on the Supply Fan Maximum
Speed (Configuration--+UNIT--+FS.MX). This is done to
maintain a constant airflow through the economizer by opening the
dampers more as the indoor fan speed is reduced or closing the
dampers more as the indoor fan speed increases.
The shape of the Economizer Minimum Position vs. Fan Speed
curve is determined by the configuration parameters: Econ Min at
25% Fan speed (Configuration--+ECON--+MP.25), Econ Min at
50% Fan speed (Configuration--+ECON--+MP.50), Econ Min at
75% Fan speed (Configuration--+ECON--+MP.75) and Econ Min
at Max Fan speed (Configuration---,ECON---,MP_X).
The Econ Min at 25% Fan speed
(Configuration--+ECON--+MP.25), Econ Min at 50% Fan speed
(Configuration--+ECON--+MP.50) and Econ Min at 75% Fan
speed (Configuration--+ECON--+MP.75) damper positions are
calculated based on the Econ Min at Max Fan Speed
(Configuration---,ECON---,MP_X) and Supply Fan Maximum
Speed (Configuration---,UNIT---,FS_X).
The Econ Min at 25% Fan speed
(Configuration--+ECON--+MP.25), Econ Min at 50% Fan speed
(Configuration--+ECON--+MP.50) and Econ Min at 75% Fan
speed (Configuration--+ECON--+MP.75) damper position are user
configurable and can be determined by setting the fan speed at 25,
50 and 75% and determining the damper position required to
maintain the Econ Min at Max Fan Speed
(Configuration--+ECON--+MP.MX) Outside air CFM through the
economizer outside air dampers. The default calculations
programmed into the PD controls is based on a side shot
economizer at 400 CFM/TON Supply Air flow with negative 0.25
in H20 pressure in the return duct.
Econ Min at Max fan Speed (Configuration--+UNIT--+FS.MN) is
set by user based on minimum required outside air ventilation
CFM required for the application. This procedure would be the
same as if this were a CV unit with the unit running at the design
point CFM. This determines the minimum position amount of
outside air CFM required when the fan is running at maximum
speed.
Configure the Indoor Fan Max Speed CFM
(Configuration--+ECON--+IDF.C) either to the supply CFM
deternfined from the fan performance tables or air balance reports.
If using fan performance tables make corrections for all installed
accessory pressure loss and use measured RPM, power and static
pressure readings to deternfine the actual Indoor Fan Max Speed
CFM (Configuration--+ECON--+IDF.C).
Economizer Position %
MAX P
20 25 50 75
ECON MIN
AT MAX
FANSPEED
POSITION
(MmNP MAX)
Minimum Configurable
Fan Speed is 20%
4PMX
;v
AQ/dl'j for DqYsj
I_ Fan Speed %
100
MINIMUM
IAQ
DAMPER
POSITION
(AO. MN)
100 700 INSIDE/OUTSIDE CO2
/ DIFFERENTIAL
AQ AQ
DIFFERENTIAL DIFFERENTIAL
LOW (AQD.L) HIGH (AQD.H)
C09145
Fig. 8 - Economizer Minimum Position
If the indoor fan is not operating, the econonfizer will be fully
closed, 0% open.
Ventilation Mode
If the space temperature falls 0.5F below the Occupied Cool Set
Point (Setpoints-+OCSP) the compressor will turn off, the indoor
fan speed will be set to the Vent Mode Fan Speed
(Configuration-+UNIT-+FS.VM) and the econonfizer will open
to the position that will supply nfinimum ventilation air at the
configured Vent Mode Fan Speed
(Configuration-+UNIT-+FS.VM). Default Vent Mode Fan Speed
(Configuration-+UNIT-+FS.VM) is 50%. Configuring the Vent
Mode Fan Speed (Configuration-+UNIT-+FS.VM) lower will
provide additional energy savings in vent mode but may not
supply the required ventilation air to the conditioned space at lower
fan speeds.
Demand Control Ventilation
The 48PD units can also be equipped with optional CO2 sensors
for additional indoor air quality control. When unit is equipped
with a return duct CO2 sensor or return duct CO2 sensor and
outside air CO2 sensor the Econonfizer nfinimum position vs. fan
speed curve will be recalculated based on the CO2 level of the
return and/or outside air as shown in Fig. 8. See the Indoor Air
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